This invention relates to the field of heat dissipation devices, specifically miniature heat pipes with optimized embedded wick structures.
Increasing power density in electronic circuits creates a need for improvements to systems for transferring heat away from the circuit. Integrated circuits (ICs) typically operate at power densities of up to 17 W/cm.sup.2. The power density will increase as the level of integration and speed of operation increase. Other systems like concentrating photovoltaic arrays must dissipate externally-applied heat loads. Advances in heat dissipation technology can eliminate the current need for mechanically pumped liquid cooling systems.
Heat spreaders can help improve heat rejection from integrated circuits. A heat spreader is a thin substrate that transfers heat from the IC and spreads the energy over a large surface of a heat sink. Heat transfer through a bulk material heat spreader produces a temperature gradient across the heat spreader, limiting the size and efficiency of the heat spreaders. Diamond films are sometimes used as heat spreaders since diamond is 50 times more conductive than alumina materials and therefore require a lesser temperature gradient. Diamond substrates are prohibitively expensive, however. Heat pipes can also help improve heat rejection from integrated circuits. Micro-heat pipes use small ducts filled with a working fluid to transfer heat from high temperature devices. See Cotter, "Principles and Prospects for Micro-heat Pipes," Proc. of the 5th Int. Heat Pipe Conf. The ducts are typically straight channels, cut or milled into a surface. Evaporation and condensation of the fluid transfers heat through the duct. The fluid vaporizes in the heated region of the duct. The vapor travels to the cooled section of the duct, where it condenses. The condensed liquid collects in the corners of the duct, and capillary forces pull the fluid back to the evaporator region. The fluid is in a saturated state so the inside of the duct is nearly isothermal.
Unfortunately, poor fluid redistribution by the duct corner crevices limits the performance of the heat pipe. Fluid has only one path to return to the heated regions, and capillary forces in the duct corner crevices does not transport the fluid quickly enough for efficient operation. There is a need for a heat pipe that can spread fluid more completely and efficiently, and therefore can remove heat energy more completely and efficiently.